1. Field of the Invention
This invention relates to a nonapertured spunlaced fabric made from woodpulp and synthetic organic fibers. More particularly, the invention concerns an improved process for hydraulically entangling such fibers and the novel spunlaced fabric of improved liquid-barrier characteristics produced thereby.
2. Description of the Prior Art
Spunlaced fabrics are strong, stable nonwoven fabrics which are made by subjecting assemblies of fibers to fine columnar jets of water, as disclosed, for example, by Bunting, Evans and Hook in U.S. Pat. Nos. 3,493,462, 3,508,308, 3,560,326 and 3,620,903. These patents disclose several specific spunlaced fabrics made from assemblies of woodpulp and polyester fibers. Examples 9 and 10 of U.S. Pat. No. 3,620,903 and Examples 4 and 5 of U.S. Pat. No. 3,560,326 describe spunlaced fabrics made from assemblies of polyester staple-fiber webs and tissue-grade woodpulp-fiber paper, wherein the woodpulp-to-polyester weight ratios range from 33:67 to 75:35. Examples 13 and XIII of U.S. Pat. Nos. 3,493,402 and 3,508,308, respectively, disclose spunlaced fabrics made from assembles of kraft paper and nonbonded, continuous polyester filament webs. The use of bonded, polyester filament webs in such spunlaced fabrics is suggested by Shambelan, Canadian Pat. No. 841,938 and by Research Disclosure No., 17060, June 1978.
Spunlaced fabrics of woodpulp and polyester staple fibers have also been available commercially, as Sontara.RTM. sold by E. I. du Pont de Nemours and Company, Wilmington, Del. USA. Such a commercial fabric and its manufacture are described in Example 2 (Comparison). The fabrics have been made into surgeons' gowns and patients' drapes for use in hospital operating rooms. An important function of the fabric is to provide a barrier to the passage of liquid and inhibit the migration of liquid-borne bacteria through the fabrics.
In manufacturing woodpulp-polyester spunlaced fabrics in the past, the streams of water are jetted from orifices of 0.002 to 0.015 inch (0.051 to 0.381 mm) in diameter, located a short distance, usually about one inch (2.5 cm) above the surface of the fiber assembly. The orifices are spaced to produce at least 10, but preferably 30 to 50, jets per inch width of fiber assembly being treated (3.9 jets per cm, preferably 11.8 to 19.7). In practice, 0.005-inch (0.127-mm) diameter orifices and 40 jets per inch (15.7/cm) are commonly used. Orifices are usually supplied with water at pressures of more than 200 psi (1380 kPa) but no more than 2000 psi (13,790 kPa). The water jets subject the fiber assembly to an energy flux of at least 23,000 ft-poundals/in.sup.2 -sec (9000 J/cm.sup.2 min) and a total energy of at least 0.1 horsepower-hour per pound (0.59.times.10.sup.6 J/kg) of fabric. Sufficient energy and impact are supplied by the jets to entangle the fibers and form them into the spunlaced fabric. The entanglement treatment is performed while the fiber assembly is supported on a fine mesh screen, an apertured plate, a solid member or the like. The treatment is performed so that the resultant fabric is not apertured and appears not to be patterned, but may have a repeating pattern of closely spaced lines of fiber entanglement, called "jet tracks", which are visible under magnification.
Orifices for use in the above-described process are disclosed by Dworjanyn, U.S. Pat. No. 3,403,862 and their arrangement in staggered rows is disclosed by Contractor and Kirayoglu, U.S. Pat. No. 4,069,563. The degree of fiber entanglement produced by the process generally is proportional to the product of E times I, where E is the energy of a jet treating the fiber assembly and I is the impact force of a jet on the fiber assembly. The usual units of the energy-impact product, E.times.I, are horsepower-hour per pound mass multiplied by pounds force (Hp-hr. lb.sub.f /lb.sub.m), which when multiplied by 2.63.times.10.sup.7, are converted to Joules per kilogram multiplied by Newtons (JN/kg). The E.times.I used in a pass of a fiber assembly under a row of jets is related to process and orifice variables by the following formula: EQU E.times.I=kP.sup.2.5 d.sup.4 n/bS
where k is a constant that depends on the units of the variables, P is the supply pressure immediately upstream of the orifice, d is the orifice diameter, n is the jet spacing in numer of jets per unit width of fiber assembly being treated, b is the weight of the fiber assembly per unit surface area, and S is the speed of the fiber assembly under the jets. The total E.times.I of the process is the summation of the E.times.I of the jets during each pass of the fiber assembly under the jets.
Although the above-described nonapertured spunlaced fabrics of woodpulp and polyester fibers have generally performed satisfactorily in hospital drapes and gowns, the utility of the fabrics could be enhanced significantly by improvements in their liquid barrier properties. The purpose of the present invention is to provide such a spunlaced fabric with increased liquid-barrier properties.